<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="../vue.2.5.1.js"></script>
</head>

<body>
    <div id='app'>
        <input type="text" v-model='msg'> {{msg}}
    </div>
    <script>
        var app = new Vue({
            el: '#app',
            data: {
                msg: 'sky'
            }
        });
        app.msg = 'fly'
    </script>
</body>

</html>